The present invention relates to improvements in liquid-filtering assemblies such as industrial-type solids-removal filters useful with electroplating equipment or the like, and, in one particular aspect, to the provision of unique and advantageous back-washing or reverse-flushing innovations enabling heavy-duty filter apparatus to be repeatedly reconditioned for efficient filtering without requiring frequent disassembly and attendant losses in costs, labor and operating time.
Filtering of liquids has conventionally exploited substances such as paper, cloth, masses of particles, and porous solids, through which the liquid is passed to remove suspended impurities. In some instances, it is desirable that the liquid subject to undesirable build-up of impurities be filtered on a substantially continuous basis, as is the case in industrial electroplating, where accumulations of suspended contaminants can otherwise seriously interfere with high-quality plating activities, and where operators would like to be able to run the equipment even more efficently by avoiding frequent and prolonged interruptions occasioned by need to disassemble and replenish the filtering. In the latter connection, the cleaning and/or changing of clogged filters tends to be tedious, onerous and costly, largely because the massive pressurized, sealed, and corrosion-resistant assemblies through which the liquid must be pumped require much careful manual labor in the take-apart, filter-replacement, and reassembly procedures.
It has been known to back-wash filter media on occasion, rather than to replace them every time clogging conditions develop, by forcing water or oil-free compressed air in direction opposite to the course of flow of filtered liquid, thereby physically dislodging trapped solids for subsequent removal from the upstream side of the filter material. Such back-washing or reverse-flushing is difficult to effect by means of relatively low-pressure water as taken directly from city water supplies, and particularly where there are broad areas of filtering surfaces to be flushed. For example, one known array which involves large filtering areas within confined spacing includes a cluster of essentially rigid tubes having small perforations and each closely surrounded by a limp fibrous sleeve which entraps the unwanted suspended matter from liquid which is pressurized to flow into the perforated tubes from outside the sleeve; however, when the flow is reversed in direction, only large quantities of water at very great pumping pressures, much in excess of those commonly available from municipal water supply lines, could be expected to dislodge the contamination satisfactorily.